A number of pyrometallurgical processes of nonferrous metallurgy involve the formation of slags which have a considerable content of a nonferrous metal oxide, which must be reduced in the slag if the nonferrous metal is to be recovered.
To effect that reduction, reducing substances are introduced into the slag layer. The reduced nonferrous metal will either be in a liquid state and will settle or it will be evaporated.
The reducing agents can consist of solid, gaseous or liquid carbonaceous substances and are injected together with oxygen-containing gases into the slag layer through nozzles or lances. Solid reducing agents consist of fine-grained coal or coke. Natural gas is mainly used as a gaseous reducing agent and mainly light fuel oil as a liquid reducing agent. The reducing agents react with the oxygen to form CO and H.sub.2, by which the reduction is effected.
U.S. Pat. No. 4,266,971 and U.S. Pat. No. 4,895,595 disclose the QSL process for a direct recovery of lead from sulfide ores in an elongate horizontal reactor, in which metallic lead and a high-PbO slag phase are produced in the oxidizing zone. In the reducing zone a reducing agent in a solid liquid or gaseous state and an oxygen-containing gas are injected through bottom-blowing nozzles into the slag phase. The secondary lead thus formed flows immediately into the reducing zone and is combined therein with the primary lead.
U.S. Pat. No. 3,663,207 discloses a process for a direct recovery of lead in an elongate horizontal reactor in which a high-ZnO slag flows into the slag zone, in which natural gas or fine-grained coal are injected as reducing agents through laterally arranged nozzles into the slag so that ZnO and residual PbO are reduced and volatilized.
U.S. Pat. No. 4,741,770 discloses a method of processing mixed sulfide concentrates, which contain mainly zinc but contain also lead and copper. A matte phase which is rich in copper oxide is maintained in the oxidizing zone and the concentrate which has been fed is reacted with injected oxygen to form a slag, which contains ZnO and PbO. Coal and oxygen are injected through lateral nozzles into that slag in the reducing zone so that zinc and lead are volatilized.
U.S. Pat. No. 4,362,561 discloses a process in which the sulfide material can be melted in a melting cyclone and is discharged onto the oxidizing zone of the elongate reactor and reducing gases are blown onto the slag through lances in the reducing zone. Propane and oxygen are used, for instance, for that purpose.
U.S. Pat. No. 3,832,163 discloses a process in which sulfide copper ores are charged onto a molten bath in the oxidizing zone of an elongate reactor and are melted in that air is injected into the bath and in which reducing gases are injected through laterally disposed nozzles or through lances in the slag in the reducing zone.
U.S. Pat. No. 3,892,559 discloses a process in which copper- and zinc-containing ores, coal and air are injected through lateral nozzles into a slag bath in an elongate reactor, whereafter the resulting liquid copper matte is tapped off and the zinc is volatilized.
U.S. Pat. No. 3,723,096 discloses a process in which iron-containing nonferrous metal materials can be melted in an elongate reactor under oxidizing conditions and the nonferrous metal is reduced in a reducing zone, in which a reducing agent, such as hydrogen or coal, is blown onto the slag bath.
In all of these processes the reducing agent together with the oxygen-containing gas is either directly injected into the slag layer or is injected into the slag through a metal layer which is provided on the bottom of the reactor and is as thin as possible. But the reducing action of the reducing agent on the slag is unsatisfactory in many cases so that the reducing agent must be used in a large surplus and this may give rise to difficulties in the operation.